Organic light-emitting diodes (OLEDs) are light-emitting diodes including light-emitting layers made from organic materials. The research and development of organic materials is an important branch of the research and development of light-emitting diodes. The known organic electroluminescent materials include phosphorescent materials and fluorescent materials. OLEDs mainly based on phosphorescent mechanism have attracted tremendous attention recently, because phosphorescent materials can keep luminance for a considerable long time after excited, and the quantum efficiency thereof (theoretical value may be up to 100%) is four times of that of fluorescent materials.
However, there are two main problems involved in the phosphorescent organic electroluminescent devices:                1) compared with the known fluorescent organic molecules, it is relatively difficult to synthesize the phosphorescent organic molecules, particularly the phosphorescent organic molecules emitting blue or green light; and        2) a hole-blocking layer (hereinafter referred to as HBL) needs to be arranged between a light-emitting layer and an electron transport layer (hereinafter referred to as ETL), in order to prevent impurity and extinction of light caused by diffusion of the excited state energy from the light-emitting layer to other layers.        
Nowadays, full-color display panels of the OLEDs are made mainly by arranging red, green and blue pixels in a “side-by-side” array. However, the development of blue phosphorescent pixels badly lags behind other phosphorescent pixels, so that it is still impossible to use exclusively phosphorescent devices in the “side-by-side” pixel array. That is, the phosphorescent pixels need to be used in combination with the fluorescent pixels, and thus an evaporation chamber for deposition of an HBL has to be included in mass production. In such a case, the process steps cannot be integrated, which not only increases the manufacture cost and time, but also makes the manufacturing process complex.